x11fwd.c

putty

/*
 * Platform-independent bits of X11 forwarding.
 */

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <time.h>

#include "putty.h"
#include "ssh.h"
#include "tree234.h"

#define GET_16BIT(endian, cp) \
  (endian=='B' ? GET_16BIT_MSB_FIRST(cp) : GET_16BIT_LSB_FIRST(cp))

#define PUT_16BIT(endian, cp, val) \
  (endian=='B' ? PUT_16BIT_MSB_FIRST(cp, val) : PUT_16BIT_LSB_FIRST(cp, val))

const char *const x11_authnames[] = {
    "", "MIT-MAGIC-COOKIE-1", "XDM-AUTHORIZATION-1"
};

struct XDMSeen {
    unsigned int time;
    unsigned char clientid[6];
};

struct X11Auth {
    unsigned char fakedata[64], realdata[64];
    int fakeproto, realproto;
    int fakelen, reallen;
    tree234 *xdmseen;
};

struct X11Private {
    const struct plug_function_table *fn;
    /* the above variable absolutely *must* be the first in this structure */
    unsigned char firstpkt[12];	       /* first X data packet */
    struct X11Auth *auth;
    char *auth_protocol;
    unsigned char *auth_data;
    int data_read, auth_plen, auth_psize, auth_dlen, auth_dsize;
    int verified;
    int throttled, throttle_override;
    unsigned long peer_ip;
    int peer_port;
    void *c;			       /* data used by ssh.c */
    Socket s;
};

static int xdmseen_cmp(void *a, void *b)
{
    struct XDMSeen *sa = a, *sb = b;
    return sa->time > sb->time ? 1 :
	   sa->time < sb->time ? -1 :
           memcmp(sa->clientid, sb->clientid, sizeof(sa->clientid));
}

void *x11_invent_auth(char *proto, int protomaxlen,
		      char *data, int datamaxlen, int proto_id)
{
    struct X11Auth *auth = snew(struct X11Auth);
    char ourdata[64];
    int i;

    if (proto_id == X11_MIT) {
	auth->fakeproto = X11_MIT;

	/* MIT-MAGIC-COOKIE-1. Cookie size is 128 bits (16 bytes). */
	auth->fakelen = 16;
	for (i = 0; i < 16; i++)
	    auth->fakedata[i] = random_byte();
	auth->xdmseen = NULL;
    } else {
	assert(proto_id == X11_XDM);
	auth->fakeproto = X11_XDM;

	/* XDM-AUTHORIZATION-1. Cookie size is 16 bytes; byte 8 is zero. */
	auth->fakelen = 16;
	for (i = 0; i < 16; i++)
	    auth->fakedata[i] = (i == 8 ? 0 : random_byte());
	auth->xdmseen = newtree234(xdmseen_cmp);
    }

    /* Now format for the recipient. */
    strncpy(proto, x11_authnames[auth->fakeproto], protomaxlen);
    ourdata[0] = '\0';
    for (i = 0; i < auth->fakelen; i++)
	sprintf(ourdata + strlen(ourdata), "%02x", auth->fakedata[i]);
    strncpy(data, ourdata, datamaxlen);

    return auth;
}

void x11_free_auth(void *authv)
{
    struct X11Auth *auth = (struct X11Auth *)authv;
    struct XDMSeen *seen;

    if (auth->xdmseen != NULL) {
	while ((seen = delpos234(auth->xdmseen, 0)) != NULL)
	    sfree(seen);
	freetree234(auth->xdmseen);
    }
    sfree(auth);
}

/*
 * Fetch the real auth data for a given display string, and store
 * it in an X11Auth structure. Returns NULL on success, or an error
 * string.
 */
void x11_get_real_auth(void *authv, char *display)
{
    struct X11Auth *auth = (struct X11Auth *)authv;

    auth->realproto = X11_NO_AUTH;     /* in case next call does nothing */

    auth->reallen = sizeof(auth->realdata);
    platform_get_x11_auth(display, &auth->realproto,
                          auth->realdata, &auth->reallen);
}

#define XDM_MAXSKEW 20*60      /* 20 minute clock skew should be OK */

static char *x11_verify(unsigned long peer_ip, int peer_port,
			struct X11Auth *auth, char *proto,
			unsigned char *data, int dlen)
{
    if (strcmp(proto, x11_authnames[auth->fakeproto]) != 0)
	return "wrong authentication protocol attempted";
    if (auth->fakeproto == X11_MIT) {
        if (dlen != auth->fakelen)
            return "MIT-MAGIC-COOKIE-1 data was wrong length";
        if (memcmp(auth->fakedata, data, dlen) != 0)
            return "MIT-MAGIC-COOKIE-1 data did not match";
    }
    if (auth->fakeproto == X11_XDM) {
	unsigned long t;
	time_t tim;
	int i;
	struct XDMSeen *seen, *ret;

        if (dlen != 24)
            return "XDM-AUTHORIZATION-1 data was wrong length";
	if (peer_port == -1)
            return "cannot do XDM-AUTHORIZATION-1 without remote address data";
	des_decrypt_xdmauth(auth->fakedata+9, data, 24);
        if (memcmp(auth->fakedata, data, 8) != 0)
            return "XDM-AUTHORIZATION-1 data failed check"; /* cookie wrong */
	if (GET_32BIT_MSB_FIRST(data+8) != peer_ip)
            return "XDM-AUTHORIZATION-1 data failed check";   /* IP wrong */
	if ((int)GET_16BIT_MSB_FIRST(data+12) != peer_port)
            return "XDM-AUTHORIZATION-1 data failed check";   /* port wrong */
	t = GET_32BIT_MSB_FIRST(data+14);
	for (i = 18; i < 24; i++)
	    if (data[i] != 0)	       /* zero padding wrong */
		return "XDM-AUTHORIZATION-1 data failed check";
	tim = time(NULL);
	if (abs(t - tim) > XDM_MAXSKEW)
	    return "XDM-AUTHORIZATION-1 time stamp was too far out";
	seen = snew(struct XDMSeen);
	seen->time = t;
	memcpy(seen->clientid, data+8, 6);
	assert(auth->xdmseen != NULL);
	ret = add234(auth->xdmseen, seen);
	if (ret != seen) {
	    sfree(seen);
	    return "XDM-AUTHORIZATION-1 data replayed";
	}
	/* While we're here, purge entries too old to be replayed. */
	for (;;) {
	    seen = index234(auth->xdmseen, 0);
	    assert(seen != NULL);
	    if (t - seen->time <= XDM_MAXSKEW)
		break;
	    sfree(delpos234(auth->xdmseen, 0));
	}
    }
    /* implement other protocols here if ever required */
    return NULL;
}

static void x11_log(Plug p, int type, SockAddr addr, int port,
		    const char *error_msg, int error_code)
{
    /* We have no interface to the logging module here, so we drop these. */
}

static int x11_closing(Plug plug, const char *error_msg, int error_code,
		       int calling_back)
{
    struct X11Private *pr = (struct X11Private *) plug;

    /*
     * We have no way to communicate down the forwarded connection,
     * so if an error occurred on the socket, we just ignore it
     * and treat it like a proper close.
     */
    sshfwd_close(pr->c);
    x11_close(pr->s);
    return 1;
}

static int x11_receive(Plug plug, int urgent, char *data, int len)
{
    struct X11Private *pr = (struct X11Private *) plug;

    if (sshfwd_write(pr->c, data, len) > 0) {
	pr->throttled = 1;
	sk_set_frozen(pr->s, 1);
    }

    return 1;
}

static void x11_sent(Plug plug, int bufsize)
{
    struct X11Private *pr = (struct X11Private *) plug;

    sshfwd_unthrottle(pr->c, bufsize);
}

/*
 * When setting up X forwarding, we should send the screen number
 * from the specified local display. This function extracts it from
 * the display string.
 */
int x11_get_screen_number(char *display)
{
    int n;

    n = strcspn(display, ":");
    if (!display[n])
	return 0;
    n = strcspn(display, ".");
    if (!display[n])
	return 0;
    return atoi(display + n + 1);
}

/* Find the right display, returns an allocated string */
char *x11_display(const char *display) {
    char *ret;
    if(!display || !*display) {
	/* try to find platform-specific local display */
	if((ret = platform_get_x_display())==0 || !*ret)
	    /* plausible default for all platforms */
	    ret = dupstr(":0");
    } else
	ret = dupstr(display);
    if(ret[0] == ':') {
	/* no transport specified, use whatever we think is best */
	char *s = dupcat(platform_x11_best_transport, ret, (char *)0);
	sfree(ret);
	return s;
    } else
	return ret;
}

/*
 * Called to set up the raw connection.
 * 
 * Returns an error message, or NULL on success.
 * also, fills the SocketsStructure
 */
const char *x11_init(Socket * s, char *display, void *c, void *auth,
		     const char *peeraddr, int peerport, const Config *cfg)